In a number of fields of activity there is need for analysis of motion and its effects. Flexing, turning or similar motions can require detection, analysis or monitoring in various sizes and amplitudes from very large to very small and from very slow to extremely fast. For example, it has been found that when turbine or compressor blades rotate at a high rate of speed they vibrate, and it is difficult to monitor and therefore difficult to analyze the vibration in order to determine and correct the cause.
In the past the problem of blade flutter has generally been investigated either by examination under stroboscopic illumination or by means of mirrors secured to the blades and employed to reflect a light beam as a blade passes a light source. Although these prior methods are valuable research and investigation tools, they nevertheless have shortcomings. For example, using mirrors, stroboscopic illumination or other methods it has been difficult to analyze blade flutter through a continuous path the motion. A strobe light, for example, may clearly show the position of a fast moving blade, but only at the instant of illumination. Similarly a moving mirror reflects a light signal but only as the mirror moves through the point of illumination.
A still further method of monitoring motion or change or position of shape is by means of holography. In one system of holography it is possible to record a shape or structure in a first condition of stress by holographic means and compare this first shape of structure against a second shape of structure in a second condition of stress. Again, however, the holographic methods have not been successful in monitoring an object through a continuous path of motion.
In other fields of endeavor it is also desirable to detect, measure or otherwise monitor the motion of an object primarily at rest or an object which moves through a principal path of motion while the object or parts thereof also undergo motion with respect to each other. For example, an object at rest such as a building may be monitored to detect and analyze sway or an object moving through space may rotate or otherwise turn on itself, as does an airplane, a glider or the like, and such motion can be monitored.